Thallus main branches terete, secondary branches occasionally partially compressed but not distinctly flattened, smooth or foveate, usually 5-20 cm long, brownish-grey to grey; soredia absent; medulla compact sometimes coalescent, usually ochre to brownish or in lower branches often dark brown. Ascomata present, circular in outline but often with undulating margin, sessile with constricted base, rarely immersed; ascospores, 22-27 x 5-6 µm (average=23 x 5.5 µm). Spot tests: medulla K-, C-; cortex K-, C- or C+ red; disc C+ red. Secondary metabolites erythrin, galapagin, portentol, protocetraric acid, roccellic acid, roccellin, acetyl-portentol (Follmann & al., 1993).
Distribution and habitat. Roccella galapagoensis is endemic to and evenly distributed across the Galapagos Islands. It grows in coastal regions on the vertical rocks and cliffs. It has never been found corticolous.
Notes. Roccella galapagoensis is characterized by its fertile, non-sorediate thallus as compared to the otherwise morphologically identical sterile, sorediate species R. margaritifera, R. nigerrima and R. lirellina. Roccella galapagoensis is a very plastic and variable species, morphologically, chemically and genetically. It contains numerous either C+ red or C- chemotypes without any clear morphological discontinuities to distinguish between them. All chemotypes are evenly dispersed geographically.